CIB3 is a calcium- and magnesium-binding protein that functions as an auxiliary subunit of the mechanotransduction (MET) channel in inner ear hair cells. It binds to transmembrane channel-like proteins (TMC1/2) through conserved hydrophobic interactions, structurally resembling auxiliary subunits of voltage-gated potassium channels 1. In cochlear hair cells, CIB3 can functionally substitute for CIB2, and calcium binding to CIB3 modulates its interaction with TMC1, acting as a calcium sensor that regulates channel localization and function 2. CIB3 jointly participates with CIB2 in regulating balance in the vestibular system 3. Pathogenic variants of CIB3 are associated with various forms of hereditary cataract, cochleosaccular degeneration-cataract syndrome, and early-onset non-syndromic cataract. Mouse models lacking both CIB2 and CIB3 display circling behavior, suggesting roles beyond auditory and vestibular function 4. At the population level, a genome-wide meta-analysis identified CIB3 among genes associated with psychological resilience in a German cohort 5. The multifunctionality of CIB3 reflects its participation in calcium-dependent signaling networks affecting sensory and neurological systems.